Ceiling or overhead transport vehicles which are sometimes used in, for example, an article transport facility transport articles by traveling along a pair of travel rails and a guide rail installed above the travel rails. In such an article transport facility, oscillations may occur in ceiling transport vehicles during traveling if the travel rails or the guide rail are not installed properly. Therefore, it is important to have the travel rails and the guide rail properly installed. To this end, it is preferable that the installed state of the rails can be inspected simply and reliably. A rail inspection device used for this purpose is disclosed in, for example, JP Publication of Application No. 2006-290177 (Patent Document 1).
The rail inspection device of Patent Document 1 is configured to detect the size of any step at a joint of two travel rail segments which are adjacent and lined up against each other along the direction in which the rail extends (an example of a installed state of a first rail and a second rail). More specifically, a laser range finder is provided in a travel carriage of the ceiling transport vehicle which travels along the travel rails. And the vertical distance from the travel carriage to a travel rail is measured by this laser range finder. However, while it is important for each travel rail to extend continuously without a step at joints, it is equally important for the pair of travel rails to have a proper spacing between them and for the guide rail to have a proper positional relationship with a travel rail.
Conventionally, in order to inspect whether a guide rail has a proper positional relationship with a travel rail, the distance along the lateral width direction between the travel rail and the guide rail is measured using an inspection jig that includes a depth gauge as shown in FIG. 12. More specifically, to measure the distance between the travel rail and the guide rail, a worker presses one end of the L-shaped inspection jig against the guide rail and measures the “depth” to the travel rail with the depth gauge attached to the other end. This method involving such manual operation is not only inefficient, but also depends highly on the worker's skill to take measurements, making it more likely to have variations in accuracy in the inspection.